The invention of this application relates in subject matter to concurrently filed application Ser. No. 873,638 entitled "Crossover Duct" in the name of Hsin-Tuan Liu.
This invention relates to machines such as turbine engines having multiple stage compressors. More specifically, this invention relates to a pneumatic crossover duct for providing flow-efficient communication between adjacent stages of a multiple stage compressor.
In the prior art, multiple stage compressors are found in a wide variety of applications. For example, a dual or multiple stage compressor is commonly used for supplying compressed charge air to a combustor section of a turbine engine. That is, ambient air is compressed by a first compressor, and then ducted to a second or subsequent compressor for obtaining increasingly higher levels of compression. Then, the highly compressed charge air is supplied to the engine combustor section including a combustion chamber for admixture with a suitable turbine fuel. The air-fuel mixture in the combustion chamber is ignited, and the hot products of combustion are utilized to rotate one or more turbine wheels at high speeds to obtain a relatively high power engine output.
In many multiple stage compressors, one or more centrifugal-type compressor wheels are commonly used. Such compressor wheels function to convert an axially entering gas stream into a radially outwardly directed compressed stream. With centifugal compressor wheels, a generally annular pneumatic crossover duct is necessarily provided between compressor stages for turning the compressed gas from a radially outward direction back toward the next compressor stage in series for further compression. In such pneumatic crossover ducts, aerodynamic considerations are of high importance in that it is desirable to couple the compressed gas stream to subsequent compressor stages with a minimum of flow turbulence, and a minimum of efficiency and pressure losses.
Crossover ducts in the prior art typically comprise one or more duct wall members forming a generally U-shaped gas flow path between compressor stages, and including a plurality of relatively thick vanes along the flow path. The vanes serve to position the wall members in approximately the desired aerodynamic configuration, and provide the duct wall members with structural rigidity. In some duct constructions, the vanes are disposed along the curved end portion, or turning bend, of the duct for assisting in turning the gas flow. See, for example, U.S. Pat. No. 3,361,073. such positioning of the vanes, however, has been found to interfere to some degree with air flow, and thereby does not result in an optimum aerodynamic configuration. Other prior art duct constructions have substituted the vanes in the turning bend with separate sets of diffuser vanes and deswirl vanes in the gas entrance and gas exit portions, respectively, of the duct. See, for example, U.S. Pat. Nos. 2,661,594; 2,797,858; 2,827,261; 2,967,013; and 3,409,340. However, this has required that relatively thick diffuser vanes be positioned in the gas entrance portion of the duct in order to assure the structural rigidity of the duct. Aerodynamically, the use of thick diffuser vanes results in undesirable efficiency of gas flow and undesirable pressure losses.
This invention overcomes the problems and disadvantages of the prior art by providing a structurally sound crossover duct having a vaneless turning bend configured to maximize efficiency and to minimize pressure losses, and including thin diffuser vanes shaped aerodynamically for improved flow efficiency and reduced pressure loss characteristics.